CHANGES IN HYDROGEN-ION CONCENTRATION PRO¬ 
DUCED BY GROWING SEEDLINGS IN ACID SOLU¬ 
TIONS 1 
By JehiEL Davidson, Associate Chemist, and Edgar T. Wherry, Chemist in Charge , 
Crop Chemistry Laboratory, Bureau of Chemistry, United States Department of 
Agriculture 
INTRODUCTION 
The importance of the reaction (the active acidity or alkalinity) of the 
medium in plant life, as well as in biological processes in general, has 
long been recognized. Studies in this field, however, have gained an 
impetus with the introduction of improved and delicate methods for 
estimating hydrogen-ion concentration. 
Taking advantage of the ease of manipulation which characterizes 
these methods, agricultural investigators and botanists have secured 
a great many data on the relation between plants and the reaction of 
the medium in which they grow. Much of the recent work, undertaken 
for the purpose of establishing fundamental principles, has been con¬ 
ducted with nutrient solutions of known composition and with seedlings 
under conditions involving the least interference from unknown disturbing 
factors. 
Most of the investigations thus far reported have dealt primarily 
with the effect of the reaction of the medium on plant growth, their 
ultimate goal being the determination of the specific optimum reaction 
of the medium for every cultivated plant. Only a few investigators 
have attacked the problem from the opposite side, studying the effect of 
the plant on the reaction of the growth medium. This side of the 
problem, however, is of the highest importance, as it may throw light 
on the causes of soil acidity under natural conditions, a knowledge of 
which will greatly facilitate the study of the means of controlling the 
reaction of the soil under cultivated plants. The work here reported 
was designed primarily to study the effect of plant growth on the medium. 
PREVIOUS WORK 
Only a few investigators whose work has a direct bearing on the 
subject matter of this article will be quoted here. 
In 1904 Veitch ( 11 ) 2 reported the effect of several kinds of plants on 
the reaction of the soil. In six years oats followed by buckwheat 
decreased the “total apparent acidity,” as determined by the Veitch 
method (jo), of nearly all the soils, some of the soils originally acid 
giving an alkaline reaction. On the other hand, beans followed by 
’Accepted for publication Nov. i, 1923. Presented in abstract at the meeting of the American Chemical 
Society in New Haven, April 6, 1923. 
s Reference by italic numbers is to the literature cited on page 217. 
Journal of Agricultural Research, 
Washington, D. C. 
(207) 
Vol. XXVII, No. 4 
Jan. 26, 1924 
Key No. E-27 
